Stress mirror polishing for future large lightweight mirrors: design using shape optimization.

This study proposes a new way to manufacture large lightweight aspherics for space telescopes using stress mirror polishing (SMP). This technique is well known to allow reaching high quality optical surfaces in a minimum time period, thanks to a spherical full-size polishing tool. To obtain the correct surface's aspheric shape, it is necessary to define precisely the thickness distribution of the mirror to be deformed, according to the manufacturing parameters. We first introduce active optics and stress mirror polishing techniques, and then we describe the process to obtain the appropriate thickness mirror distribution, allowing to generate the required aspheric shape during polishing phase. Shape optimization procedure using PYTHON programing and NASTRAN optimization solver using finite element model (FEM) is developed and discussed in order to assist this process. The main result of this paper is the ability of the shape optimization process to support SMP technique to generate a peculiar aspherical shape from a spherical optical surface thanks to a thickness distribution reshaping. This paper is primarily focused on a theoretical framework with numerical simulations as the first step before the manufacturing of a demonstrator. This two-step approach was successfully used for previous projects.

Elastic bending of variable curvature mirrors: validation of a simplified analytical method.

This work explores the variable curvature mirror's (VCM) elastic bending rules through modeling it as a thin elastic plate with an exponential thickness distribution actuated with a uniform pressure under simply supported boundary conditions. By using the small-parameter method, the general analytical expression of a plate's deflection is worked out. The results calculated by the analytical solution are compared to the finite element analysis of a VCM model with the same specific parameters. We demonstrate that the two have a good correlation with the each other. This analytical solution is an effective way to predict a VCM's deflection.

Methodology to design optical systems with curved sensors.

Curved sensors are a suitable technological solution to enhance the vast majority of optical systems. In this work, we show the entire process to create curved sensor-based optical systems and the possibilities they offer. This paper defines the boundaries of the reachable curvatures for a full range of monolithic sensors. We discuss how the curved focal plane shape is related to the imaged scenes and optical parameters. Two camera prototypes are designed, realized, and tested, demonstrating a new compact optical architecture for a 40 deg compact objective as well as a wide-field fisheye zoom objective using a convex sensor to image a 180 deg field of view.